Gas purification process

ABSTRACT

In a process for removing CO2 and like acid gases from a gaseous mixture by an absorption solution which is regenerated by boiling above atmospheric pressure, the improvement which is removing the boiling solution from the regeneration and injecting it into an expansion zone, whereby a stream of vapor results containing a portion of the CO2 etc. from the absorption solution which, being cooled with a reduced CO2 etc. content is returned to the absorption zone. The stream of vapor is vented.

United States Patent 1 Giammarco 1 Jan. 30, 1973 54 GAS PURIFICATIONPROCESS 2,886,405 5/1959 Benson et al. ..23/3 [76] Inventor: GiuseppeGiammarco, San Marco 5 3242, Piazzale Moron", Venice Italy PrimaryExaminer-Earl C. Thomas [22] Filed: Oct. 13, 1969 Att0rney-S'ughrue,Rothwell, Mion, Zinn 8L Macpeak [2i] Appl. N0.Z 865,852 57 ABSTRACT In aprocess for removing CO and like acid gases [52] [1.5. CI ..423/220 froma gaseous mixture by an absorption Solution [5i] III!- Cl. ..B01d whichis regenerated y boiling above atmospheric [58] held of Search pressure,the improvement which is removing the boil- 23/4 ing solution from theregeneration and injecting it into an expansion zone, whereby a streamof vapor results [56] References cued containing a portion of the COetc. from the absorp- UNITED STATES PATENTS tion solution which, beingcooled with a reduced CO etc. content IS returned to the absorptionzone. The 2,943,9l0 7/1960 Gia'mmarco ..23/2 R stream of vapor isvented. 3,039,845 6/]962 Steinrotter ....23/2 R 2,860,030 I 1/1958Goldtrap et al. ..23/2 3 Claims, 22 Drawing Figures PAIEYNTEBJMBO I9733.714.327 SHEET 2 OF 8 Sol'n: ['IEA =2,5 Mo'L/l final vaiue 0.20 0.300.40 0.50 .50 lmtlal value M01 Cog/M01 "EA n rmal Hash m --conlroned Hash 126 c Carbonabakion degree PercenT heaT reduch on on normal valuesPATENTEUJAIBIO ms 3. 714.327 SHEET 7 OF 8 Fig.19

Fig. 20

GAS PURIFICATION PROCESS FIELD OF THE INVENTION DESCRIPTION OF THE PRIORART It is well known that in the majority of cases it is suitable andmore often than not necessary for the temperature during the absorptionphase to be less than that in the regeneration phase in which thesolution is heated to boiling temperature. Consequently, by virtue ofthe aforesaid temperature difference, it is fundamentally important forthe heat expended in heating the solution from the absorptiontemperature to the boiling temperature (in other words the heatcontained in the boiling regenerated solution which emerges from theregeneration phase) to be suitably utilized for the purposes of theprocess instead of .being uselessly eliminated through a coolant which,inter alia, represents an element of cost.

Hitherto, the heat content of the boiling regenerated solution has beenused in diverse ways by the various cycles employed in industrialpractice, of which the best known are the conventional, isothermic andoptimal cycle.

In the conventional cycle, from what is known, the absorptiontemperature is substantially less than the regeneration temperature; itis also well known that by using ethanol amine solutions (MEA, DEA, TEA)or other solutions of organic compounds, in the cases of absorption ofboth C0, and H 8, the absorption temperature is close to ambienttemperature. In this cycle, it is well known that the heat content ofthe boiling regenerated solution is used for heating the exhaustedsolution before this latter is passed to the regenerator. For thepurpose, a heat exchanger and a coolant are used, interposed between theabsorber and the regenerator. However, it is a known fact that the saidheat exchanger is very expensive and alone represents a considerablepercentage of the, cost of the plant.

It would therefore be highly desirable for the conventional cycle tobemodified and improved as is one of the objects of the presentinvention so that, while the absorption phase involves temperaturesfairly close to ambient temperature, the heat exchanger mentioned may beeliminated.

The isothermic cycle does not utilize the heat in the boilingregenerated solutions. As is well known, it dispenses with the heatexchanger by virtue of the fact that the boiling regenerated solution ispassed directly to the absorber. This advantage is however cancelled outby the fact that the absorption temperatures are considerably high andgenerally higher than the socalled optimum temperatures (as definedhereinafter and corresponding to the minimim volume and the minimumheight of the absorption column), and also basically by the fact thatthe heat content of the boiling regenerated solutions, after beingpassed disadvantageously along the absorber, is finally eliminated tooutside by means of the cooler employing CO, (or other acid gases) whichmust be constructed from steel capable of withstanding the corrosiveproperties of the said .acid gases, entailing an increase in the cost ofthe plant.

it would therefore be desirable for the isothermic cycle to be modifiedand improved, as is the object of the present invention.

The optimum cycle is characterized by the fact that the boilingregenerated solution is slightly cooled (generally to to C in the caseof mineral solutions, such as solutions of ordinary or activatedcarbonate) so that the solution, descending along the absorberandbecoming heated by the heat of reaction and the heat contributed by thegas which is to be purified, reaches a temperature of at least 98 to C,sufficiently to be passed directly to the regenerator with no need for aheat exchanger. This produces the advantage of eliminating the heatexchanger from the conventional cycle; another advantage is that theheat furnished by the functioning of the cycle is not entirelyeliminated by the CO cooler, as in the isothermic cycle and constructedin stainless steel, but is in part eliminated by means of theregenerated solution cooler which on the other hand is more economicallyconstructed in carbon steel and is moreover less expensive by virtue ofa more favorable difference in temperature.

it is also well known that one of the characteristic features of thiscycle is the fact that the absorption temperature is close to theso-called optimum temperatures (hence the name optimum cycle). it is aswell to recall the fact that an increase in temperature improves the Kgacoefficient of the alkaline carbonate solutions, whereas on the otherhand the CO, and H 8 vapor tensions rise. The aforesaid two effects,opposite and contrasting, of the rise in temperature, determine thesocalled optimum temperature to which-as defined by Sherwood-correspondthe best conditions of absorption, in other words the minimum volume andminimum height of the absorption column. The optimum cycle can utilizethe heat in the boiling regenerated solution since the solution cooleris for practical purposes replaced by a heat exchanger-recuperator, inwhich the boiler feed water is heated.

It would be desirable for the optimum cycle, while retaining theaforesaid characteristic features, to be modified and improved, as isthe object of the present invention, so that the heat contained in theboiling regenerated solutions is better utilized for the useful purposesof the purification process itself.

The object of the present invention is to use the heat content of theboiling regenerated solutions in order to improve the degree ofregeneration of the solutions themselves. Another object of theinvention is to diminish the supply of heat necessary for operation ofthe cycle.

Another object of. the invention is partly or completely to eliminatethe heat exchanger between hot regenerated solution and cold exhaustedsolution in cases where absorption is carried .out at a temperaturelower than the regeneration temperature. Another object of the presentinvention is considerably to reduce the cost of the plant.

SUMMARY OF THE INVENTION The present invention is based on the fact thatthe heat contained in the regenerated solution, hot or boiling, isextracted in the form of a stream of vapor which is basically used inorder to extract from the regenerated solution part of the C0, and/orother acid gases contained therein, so improving the degree ofregeneration.

The extraction of the vapor flux is carried out by various methods, assuggested in the description of the present invention, and consistingbasically in subjecting the solution to a drop in pressure or to atreatment with inert gases.

As stated above, extraction of the vapor flux is facilitated by passingit into a colder zone where the said vapor condenses and preferably bybringing it into intimate and direct contact with the colder exhaustedsolution originating from the absorption column, for the purpose ofheating this. In this way, the heat contained in the hot regeneratedsolution passes to the cold exhausted solution more simply andeconomically than by means of the expensive heat exchanger hitherto usedin prior art arrangements and which can therefore be wholly orcompletely eliminated. Furthermore, there is greater efficiency in theuse of heat in that, as will be specified hereinafter under e), thesolution can be estimated to eliminate a quantity of CO, greater thanthat eliminated by using the heat exchanger.

A further advantage resides in the fact that the passage of vapor fromone solution to the other occurs spontaneously and with no consumptionof energy, this until such time as the two solutions have reachedequality of temperature, and more precisely equality of the respectivewater vapor tensions.

BRIEF DESCRIPTION OF-TI-IE DRAWINGS FIG. 1 5 show initial and finalcarbonate contents of specific absorbent solutions when flashed normally(i.e., finstantaneously) and controllably (i.e., gradually);

FIG. 6 shows the percent heat reduction realized when the controlled,rather than the normal, flash is utilized for a potassium arsenitesolution;

' FIGS. 7-1 1 show initial and final carbonate contents of specificabsorbent solutions desorbed using inert gases, both normally and undercontrolled conditions;

FIG. 12 shows the final carbonate contents of various absorbentsolutions when passed against a 11,0/00, heating stream at varioustemperatures;

' FIG.*13 shows the initial and final carbonate contents of a potassiumarsenite solution flashed by vacuum;

FIG. 14 shows the variation in final carbonate content with temperatureof various potassium arsenite solutions having varying initial carbonatecontents, during regeneration with an inert gas; and

FIGS. 15-22 illustrate apparatus which may be employed in the practiceof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is now intended to set forthinformation concerning the extraction of the vapor flux from theregenerated solution and its use to eliminate part of the CO, and/orother acid gases contained in the solution itself. v

This advantage is perhaps the most important in the present invention,by virtue of the fact that the better degree of regeneration which isthus achieved would, according to the hitherto known state of the art,require the supply of close to double the amount of heat to theregenerating column.

Theabove-mentioned regenerative improvement in regenerated solutions byusing the heat contained in the solutions themselves is a new fact andone of which there has been no record in the prior art, and moreover itis surprising both in itself and also by virtue of the fact that theheat extracted from the solution and consumed by the aforesaidimprovement may in certain cases even be less than that which normallyought to be supplied .to a conventional regenerating column in order toachieve the same effect.

Indeed, as claimed in the present invention, the aforesaid improvementin the degree of regeneration requires that the alkaline carbonatesolutions contain particularly effective activators (preferablyactivators of an acid nature such as As,0,, glycine (amino acids) andthe like); furthermore, it requires extraction of the vapor from the hotor boiling regenerated solution to be carried out with the specialapparatus which will be suggested and described hereinafter or the otherapparatus which is the object of Italian Pat. application No. 51,679which is a patent linked with the present.

1. One of the most simple and easily applied methods of extracting thevapor flux from the hot or boiling regenerated solution and hereafterreferred to as Case I is that of expanding the regenerated solutionitself from an above atmospheric pressure to a pressure close toatmospheric.

This is the case which arises in industrial practice, when theregenerating column is functioning at above atmospheric pressure inorder to produce pressurized C0,, as is ideal if the CO, is intended forurea production. Generally, a pressure of approx. 2 to 2.5 atm. abs. isselected. In such a case, a simple or activated alkaline carbonatesolution boils at a temperatureof approx. to C and leaves theregenerating column at the above-mentioned temperature. i

A similar case arises even if the regenerating column is a column withplates which, as is well known, give rise to an increase in pressure atthe bottom of the regenerating column and a consequent rise inthe'boiling temperature of the solution; In these cases, the vapor fluxis easily extracted from the regenerated solution by causing thesolution itself to expand to'.atmospheric pressure and with no needformechanical or similar apparatus which is nevertheless required in theother cases described hereinafter.

The regenerative effect which is obtained by extracting the vapor fluxfrom the solution has been the object of appropriately conductedexperiments in which the best known and most important absorbentsolutions have been used, such as the solutions of potassium arsenite,solutions of alkaline carbonate activated by the addition of glycin, orby the addition of DEA, solutions of simple potassium carbonate,solutions of monoethanol amine or other ethanol amines.

The aforesaid solutions have been used in experiments at temperatures inall cases regulated initially at 126C, the solutions being subjected toa gradual and slow reduction in pressure until atmospheric pressure isattained. r

The best and simplest method used in the experiments was that of passingthe regenerated solution at the initial temperature of 126C to thebottom of a vessel preferably provided with filling material and filledwith liquid to a height of 8 to 10 m. As the solution rises upwardlyalong the aforesaid vessel there is a reduction in pressure acting onthe liquid. This reduction in pressure is due to the decreasing heightof liquid in the column that remains above the solution as it movesupwardly. Consequently, as the pressure progressively and graduallydecreases, there develops a vapor flux. The period of dwell of thesolution in the expansion vessel has been regulated so that the vapordevelops and acts on the solution in the same way and in the same timeas would arise in the reboiler of a conventional regenerating column.Other methods have been used for the same purpose, as described inItalian Pat. application No. 51,679. The best experimental results wereobtained by discharging the CO, to the outside as the vapor extracted itfrom the solution (see FIG. 21). Other comparative experiments wereconducted for each solution and for each case, the solution beingnevertheless caused to expand simply and instantaneously. 1

The results of the experiments are set out in FIGS. 1, 2, 3, 4, 5, eachrelative to a type of solution, the nature and composition of which ismarked on the figure itself. The abscissae indicate the initial degreesof carbonatation of the solution, the ordinates the final degrees ofcarbonatation.

As stated above, the initial temperature was regulated to 126C and thefinal temperature, in other words when the solution reaches atmosphericpressure at the top of the expansion vessel, is shown at the variouspoints on the graph itself.

In each figure, the top graph (broken line) represents the resultsobtained by causing the solution to expand simply and instantaneously(normal flash); the bottom graph (solid line) represents the resultswhen the solution is made to expand as stated above (controlled flash).

Thus, for example (see FIG. 1), a solution of potassium arsenite, 200g/l K 0 and 140 g/l As O with an initial temperature of 126C and 20percent carbonatation, expanding to atmospheric pressure simply andinstantaneously, improves its degree of carbonatation to 18.5 percent,cooling to 100.5C, so that the regenerative effect is virtuallynegligible. On the other hand, when the solution is expanded by themethod specified above, the solution improves its degree of regenerationto 3.5 percent and cools to 104C.

This result is extremely interesting and is of great practicalimportance both because the 3.5 percent degree of carbonatation thusobtained makes it possible to achieve with a single-stage cycle a degreeof purity which is generally only obtained by using a two-stage cycle,because it is sufficient in an industrial plant to regenerate thesolution to a 20 percent degree of carbonatation by supplying externalheat and then improving it to 3.5 percent by causing the solutiongradually to expand to atmospheric pressure and by using the heatcontained in the solution itself. This makes it possible to reduce theamount of external heat supplied to the reboiler of the regeneratingcolumn by approximately half.

The saving on heat obtained as stated above by the present invention isrevealed in diagram 6 which relates to the use of potassium arsenitesolutions, which are widely used industrially.

In FIG. 6, the abscissa represents the percentage saving on the supplyof heat, the ordinate represents the degree of carbonatation of thesolution before expansion, while the final degree of carbonatation afterexpansion is marked on the various points of the graph.

Thus for example, a solution with an initial degree of carbonatation of15 percent and with an initial temperature of 126C, which is obtainedfrom a regenerating column to which 21,500 kg.cal./cu.m. of solutionhave been supplied, is caused to expand to atmospheric pressure, soobtaining a 2 percent degree of carbonatation (point A on the Figure).

This degree of carbonatation would have required the supply of 40,500kg.cal./cu.m. of solution of heat to the regenerating column.Consequently, the supply of heat is reduced from 40,500 to 21,500kg.cal./cu.m. of solution, in other words by 48 percent (point B of thefigure, following the broken lines).

FIGS. 2, 3, 4 and S relate to the use of other types of absorbentsolutions, these being shown on the respective figures, in other wordspotassium carbonate solutions embodying various activators or solutionsof monoethanol amine. I

By comparing the results shown on the aforesaid figures, it is revealedthat the regenerative effect is a property which alkaline carbonatesolutions acquire when activators are added. The regenerative effect isat its maximum for alkaline carbonate'solutions activated by theaddition of AS203; then it diminishes almost negligibly for solutionsactivated by 100 g/l of glycine, then drops again for solutionsactivated with 30 g/l of glycine; the drop continues for solutionsactivated by DEA and ordinary carbonate solutions. The ethanol aminesolutions also have a regenerative effect.

Finally, it is manifest that simple and instantaneous expansion does notproduce a notable regenerative effect and in fact the broken lines whichrelate to simple expansion are not substantially remote from the dottedlines which on each diagram indicate that the solution undergoes noregenerative effect during expansion.

2. Another method of extracting the vapor flux from the hot or boilingregenerated solution is to expand the tioning at a pressure virtuallyequal to atmospheric pressure. The solution which in such a case rangesin temperature from to C, is extracted from the regenerating column andmade to expand in an expansion or vaporization zone or chamber in whicha negative pressure is applied by means of a vacuum pump or otherappropriate and opportune mechanical means, preferably including anejector into which the exhausted solution emanating from the absorptioncolumn under pressure is introduced, the energy it contains beingutilized as described in Italian Pat. application No. 53,475 which islinked with the present patent application.

Another method of producing a vacuum and suggested in the presentinvention is that of using in an ejector the purge gases from N11, ormethanol synthesis, these gases being available at a pressure of 100 to300 atm.

As will be specified hereinafter, the application of vacuum to thesolution and the extraction of a vapor flux from the solution requiresno consumption of energy if, as claimed in the present invention, thevapor itself is passed into a colder temperature zone and possibly azone in which the colder exhausted solution is present, whichconsequently condenses the vapor and becomes re-heated. More detailedinformation, particularly with regard to the C0, and/or other acid gaseswhich'accompany the vapor, are given in the following section.

In this case, too, as in the present case I, demonstrative andcomparative experiments were conducted, using the best known and mostimportant absorbent solutions.

In the aforesaid experiments, the drop in pressure achieves the bestresults when carried out with apparatus similar to that mentioned incase I, or using the procedures and apparatus suggested and described inItalian Pat. application No. 51,679, which, it is repeated, is linkedwith the present patent application.

For reasons of operative convenience, the initial temperature of thesolution was fixed at 102C and the final temperature, actingappropriately on the degree of vacuum, was fixed at around 80 to 85C,which is the temperature considered most suitable for simple oractivated alkaline carbonate solutions to be passed to the top of theabsorber.

The results obtained by the experiments are completely analagous tothose in case 1 except for the fact that the regenerative effect provedto be slightly less, which must be attributed to the fact that in thiscase the temperatures in the experiments were lower which reduces theKga transfer coefficient.

By way of illustration of the foregoing statements, FIG. 13 shows theresults relative to a potassium arsenite solution; these results are inevery respect similar but slightly inferior to those of FIG. 1.

Also in this case, as in the previous case l, the regenerative effect isat its maximum for potassium arsenite'solutions, diminishing then forthe other types of less activated solutions; it drops still further forsimple carbonate solutions. Ethanol amine solutions on the other handhave in this case a lesser regenerative effect than in the'precedingcase i and this must'be attributed to the lower temperature at which thesolution is processed.

3. Another method of extracting the vapor flux from the hot or boilingregenerated solution is that of treating the solution itself withdesorbent gases, preference naturally being given to the use of gaseswhich are chemically compatible with the solution so as not to causealterations or chemical decomposition of the solution itself.Particularly indicated for the purpose are purge gases from NH, ormethanol synthesis, gas residues fromfractionating apparatus, andcombustible gases when they are free from oxygen and H,S.

For this case, too, demonstrative and comparative experiments werecarried out, the various types of absorbent solutions hitherto known inindustrial practice being used.

in the experiments, the solution had an initial temperature of 102C.This temperature was chosen for and therefore, on this basis, theresults obtained will be better than those obtained described here.

The solution was introduced into the top of a column provided withfilling material, in the bottom of which a flow of inert gases(nitrogen) was introduced on a counter current principle, the quantityof inert gases being varied over 5 to 10 times the quantity of solution.

it was however established that the best proportion of solution to inertgases was 1 5, particularly when the vapor extracted from the gascurrent was used for heating the exhausted solution.

The inert gas was supplied at ambient temperature and the experimentalprocedure was regulated so that the inert gas cooled the solution to atemperature of to 84C. For this purpose,- the flow of solution wasappropriately regulated relative to the volume and height of the column.

The experiments were carried out for every type of solution and areshown in F108. 7, 8, 9, 10 and 11.

In the said Figures, the abscissae represent the initial degrees ofcarbonatation of the solution, while the ordinates represent the degreesof carbonatation obtained at the end of the experiment.

Also indicated on the graphs of these figures are the temperatures ofthe solutions on leaving the column and also indicated, between squarebrackets, are the temperatures of the inert gas charged with H 0 and CO,emerging from the top of the column (in other in the experiments wordsthe dew point temperature).

The results set out in the aforesaid figures are analagous and similarto those obtained experimentally in case 1, controlled flash, except fora slight drop due to the fact that the solution transport coefficient-isslightly diminished by virtue of the lower temperature of theseexperiments as compared with those in case l.

in this case, it should also be noted that the regenerative effectachieved with the current of inert gases is maximum for the potassiumarsenite solutions and then diminishes gradually for the othersolutions. Even the MEA solutions have a substantial regenerativeeffect.

Further complementary experiments were carried out to ascertain the wayin which the degree of carbonatation of the solution varies as the heatis extracted from the solution, the initial temperature of which is102C, in other words as the solution cools. These results are set out inFIG. 14 and relate to the use of a potassium arsenite solutionpreselected for the experiments by virtue of its wide industrial use.

it is now intended to present and illustrate the variousmethods, theobject of the present invention, ,by which the vapor, after having beenextracted from the hot or boiling regenerated solution, together withthe CO, and/or other acid gases contained in the solution itself, isused for heating the exhausted solution.

it is worth while emphasizing two characteristic features, d) and e),which are specific features of the two aforesaid methods:

d. The passage of vaporfrom one solution to the other is spontaneous andrequires no energy consumption (although theoretically thisought toarise) until such time as the regenerated solution is at a temperatureor rather a vapor tension in 11,0 greater than that of the exhaustedsolution which receives the vapor itself. This is known in the industryand a man skilled in the art understands that the aforesaid method isquite different from that of extracting the vapor from the regeneratedsolution by means of a thermo-compressor and compressing it with thisapparatus up to a sufficient pressure and temperature for utilizationfor example in the bottom of the regenerating column. lnsuch a case, infact, there is a consumption of energy which does not arise in thepresent invention.

It should be noted however that the vapor extracted from the regeneratedsolution contains, as previously stated, a certain quantity of CO and/orother acid gases which modify the phenomenon and require a consumptionof energy for passage from one solution to the other. However, thequantity of energy involved is quite small as will be stated at the endof the section g) below.

e. During the course of studies and appropriately conducted experiments,it has been found that the heat given off by the regenerated solution tothe exhausted solution through the passage of vapor stream, as statedabove, is used mostly and more conveniently than found with the heatexchanger hitherto employed in the industry. This is due to the factthat for parity of temperatures attained in heating, the exhaustedsolution eliminates a greater quantity of CO and/or other acid gases andis therefore fed into the regenerating column under conditions morefavorable to the thermal balance thereof.

In fact, in the hitherto knownstate of the art, the heat exchanger heatsthe exhausted solution when it is still under the pressure at which itemerges from the absorber; subsequently, the solution is expanded to thepressure of the regenerator and, as is well known, the heat consumed inthis expansion is mainly expended in order to develop water vapor, thisbeing a very rapid physical phenomenon, and in a lesser quantity for thedevelopment of CO which is regulated by chemical reactions which areknown to be slow. Finally, the ratio of H vapor/CO is in considerableexcess of equilibri- Nevertheless, by employing the heating methodaccording to the present invention, the water vapor extracted from theregenerated solution condenses on the exhausted solution, heating it,and the CO, is ejected gradually as the heating takes place and finallythe ratio of H 0 vapor/degasified C0 is very close to that ofequilibrium. This reveals a better utilization of the heat, as has beenestablished and checked by appropriate experiments.

The said experiments consisted in reproducing the conditions ofoperation of the method which is the object of the present invention, infact in passing a heating flow of H 0 and CO, in various proportions, indirect contrast with an exhausted solution, in other words a solutionwith a high degree of carbonatation. For reasons of operativeconveniences, the experiments were carried out at atmospheric pressure.

The results are set out in FIG. 12, in which the ordinate represents thetemperatures of the heating stream and the abscissa represents thedegree of carbonatation at which the solution arrives after a certaintime. The graphs in the Figure itself relate respectively to solutionsof potassium arsenite, 200 g/l 1(,0 and 140 g/l As,0,, solutions ofpotassium carbonate, 250 g/l 11,0 and activated with glycine at the rateof 50 g/l and to a solution of 2.5 mols/liter MEA. As is well known, thetemperature of the heating stream depends on and determines the ratio ofl-l,O/CO, which is the dew point. Thus for example, referring to thepotassium arsenite solution, a heating stream at a temperature of C, inother words with a ratio of r o/co, equal to 2.3 (point A on thefigure), regenerates the solution to a- 29 percent degree ofcarbonatation. (point C on the figure). From experiments, it is alsoknown that the solution correspondingly acquired a temperature of 94Capprox. (point B of the figure); and here it is important to observethat from repeated experimental observations carried out for thispurpose, it is revealed that the vapor CO flow heats the solution to atemperature higher than its own. This is a fact which is probably notwidely known among men skilled in the art. For greater clarity, anexperiment was conducted involving a saline solution, boiling at 105C,as an example, which emitted vapor at a temperature of C which is theboiling temperature of the pure solvent; a flow of pure vapor, saturatedat 100C, tends to heat a saline solution towards C and thus to atemperature in excess of 100C.

Referring now to the example given above concerning a potassium arsenitesolution, it is in fact observed that in industrial practice an arsenitesolution regenerated and heated to C heats the exhausted solution up to100 to 102C. This latter, subsequently expanding before entering theregenerating column or in the upper part thereof, cools to approx. 95C,but is regenerated only up to 44 to 48 percent instead of 29 percent asin the above-described example of application of the present method.

f. The considerations raised in the two previous sections d) and e) makeit possible to establish certain criteria as to the suitability ofapplication of the various methods of the present invention.

As stated at the beginning of the description, the stream of vaporextracted from the regenerated solution, in addition to eliminating apart of the C0 and/or other acid gases contained in the solution itself(this being the basic object) can also be used for heating the exhaustedsolution with which it is brought into direct contact, so dispensingwith the need for the heat exchanger hitherto used in known techniques.

The two objects may be attained separately or jointly according to thetype of solutions used and the operative cycle in which they are used.

In many cases, the extraction of vapor from the regenerated solution hasa substantial regenerative effect, eliminating substantial quantities ofCO, and/or other acid gases from the solution itself, making it possiblenot only to reduce considerably the supply of heat necessary forfunctioning of the cycle, but also, in one stage of working, to arriveat a degree of purity in the gaseous mixture which is generally obtainedwith a two-stage plant. All this has been previously demonstrated.

This takes place in cases of strongly activated solutions, such as isthe typical case with arsenite solutions, on in cases of markedlyregenerated solutions, in the actual regenerating column itself.

In contrast, the considerable quantities of CO, and/or other acid gasesdesorbed, which accompany the vapor, lower the dew point of the heatingflow and render it less suitable for heating of the exhausted solution.Furthermore, the passage of CO, requires a certain consumption of energywhich does not happen in the case of the vapor. I

The solutions of this type are advantageously used in optimum orisothermic cycles, in which the heat exchanger does not exist or is notnecessary. Particular examples of this application are given in examples1, 3, 6. In these, it has been found suitable for the flow of vaporextracted from the regenerated solution to be condensed in suitablecoolers or discharged to outside.

Vice versa, the solutions in which the regenerative effect is poor andin other words in which the vapor extracted from the regeneratedsolutionis accompanied by small quantities of C0,, offer the bestconditions for heating of the exhausted solution and for partial ortotal abolition of the heat exchanger. This is the case withnon-activated solutions, such as simple carbonate solutions or ethanolamine solutions and in general the solutions which have been stronglyregenerated in the regenerator proper. The solutions used specificallyfor absorption of I-I,S are the most suitable for this case in that thevolumes of l-I,S absorbed per volume of solution are in the majority ofcases of a small amount and therefore. the vapor extracted from theregenerated solution is in a very high concentration.

The above-mentioned solutions are preferred in conventional cycles andin fact in any cycles in which there is a difference in temperaturebetween the absorption phase and a regeneration phase and in other wordsin cycles in which the heat exchanger has been used hitherto.

Particularly advantageous are cases in which both the aforesaidadvantages can be used at the same time. Examples of these cases aregiven in examples, 2, 4, 5.

g. In the practical application of the present invention, the vaporwhich is extracted from the regenerated solution is brought into contactwith the exhausted solution by mixing apparatus (mixing or reheatingzone), so that this can take place in a single stage, as is sufficientin the majority of cases, or in a plurality of successive stages if itdesired that the exhausted solution be heated to a temperature close tothat of the regenerated solution. This'can be carried out with theapparatus shown in FIG. 21 or with similar apparatuses which are easilyavailable to a man skilled in the art. In the case of the apparatus inFIG. 21, the flow of vapor is extracted from theregenerated solution insuccessive stages while the latter is rising along the column shown onthe right of the figure; the vapor extracted at each 1 individual stageis passed to the exhausted solution heat from the regenerated solutionto the exhausted solution takes place via two zones, generally twocolumns provided with filling material or some other similar apparatus,traversed respectively by the regenerated solution and by the exhaustedsolution; the current of inert gases passes first through the heating orvaporization zone which is traversed by the regenerated solution, whereit becomes heated and humidified at the expense of the heat removed fromthe regenerated solution and subsequently it passes into the heating ormixing zone which is traversed by the exhausted solution in which itheats the solution itself, condensing the vapor entrained and at thesame time producing a pre-regeneration of the exhausted solution asindicated in FIG. 19 and in example 5.

In the practical application of the present invention, it is observedthat the regenerated solution, in reference to cases 1 and 2, in whichthe vapor is extracted by decompression, it at a lower pressure than theexhausted solution. In this'case, if it is not desired to use theejector, it is necessary to use a mechanical propulsion means which isgenerally located between one column and the other as indicated in FIG.18.

As stated previously, the passage of steam from one solution to theother does not consume energy, whereas energy is consumed in the passageof the CO, which'accompanies the vapor extracted from the regeneratedsolution. The amount of energy consumed is small.

In fact, even with the object of guiding a man skilled in the art, inmaking his choice from among the aforesaid criteria of suitability, itis pointed out that the expenditure of energy for passage of the CO,which accompanies the vapor, from the regenerated solution to theexhausted solution, is calculated theoretically at 0.013 Kw/hr. X 1,000calories in the case of an alkaline arsenite solution which, expandingfrom 126C to 104C, is regenerated from a 20 percent carbonatation levelto 3.5 percent, developing a heating flow with a proportion of H,Ovapor/CO, of 5.4.

On the other hand, in the case of a monoethanol amine solution of 2.5mol/liter, which expands from 126C to 104C, regenerating from 20 percentcarbonatation to 15 percent, the consumption of power is calculated at0.0047 Kw/hr. per 1,000 calories transported from one solution to theother.

h. Finally, it should be noted that, as has been stated several timesalready, the extraction of the vapor stream cools the regeneratedsolution. As is well known to a man skilled in the art, this has theadvantage that the solution is passed to the absorption column, partlyor wholly eliminating the cooler.

i. The present'invention can obviously be applied to EXAMPLE 1 Withreference to FIG. 15, a plant for eliminating CO, from a gas at 28 atm.with an initial concentration of 18 percent C0, is washed with analkaline arsenite solution consisting of 200 g/l K,0 and 140 g/l As,0,.

The exhausted solution emanating from the bottom of the absorber ispassed to the top of the regenerating column R, operating at 8 atm.,where it is regenerated to a level of 20 percent carbonatation by thesupply of 21 ,000 Kcal/cu.m. of solution.

The regenerated solution is extracted from the bottom of the regeneratorat a temperature of 126C which is the boiling temperature correspondingto the working pressure of the regenerator itself, and it issubsequently passed to the expansion column C which in FIG. is situatedon the left of the regenerating column R. This column is equipped withplates or filling material and is filled to about 8 m by the solutionitself. This latter, as it rises along the column, develops vaporgradually and progressively, which eliminates part of the CO containedin the solution.

When expansion is complete, at the top of the column C, the solution hasreached a degree of 3.5 percent of carbonatation and its temperature is105C.

The solution is drawn off at the top of the expansion column by means ofthe pump P and is fed back to the absorption column A suitably cooled bya subsequent cooler in one stream only or in split stream according tothe purification required.

The solution then passes through the absorption column from the bottomof which it is drawn off with a degree of carbonation of 66.5 percentand is passed directly to the regenerating column.

It will be observed that the solution is regenerated in the regeneratingcolumn to a degree of carbonatation of percent by the supply of heat tothe extent of 21,000 kg.cal./cu.m. of solution, while to obtain a degreeof 3.5 percent carbonatation in the solution such as emerges from theexpansion column C, it would have been necessary to supply heat to theextent of 37,400 kg.cal/cu.m. of solution, in other words virtuallytwice the amount.

In the example it has been shown that the supply of heat in thereboiler, is carried out by using the process gas, which emergesfrom-the reboiler itself at a temperature of approx. 135C. It isconsidered suitable to pass it at the same temperature to the bottom of.the absorber where it heats the solution to a temperature suitable forthe thermal balance of the regenerator. This has been described inItalian Pat. application No. 53,496 and its supplement No. 51,505, andin Patent application No.53475-A/68.

It will be observed that the solution absorbs approx. 30 parts CO percu.m. of solution; the heat consumed is 700 kg.cal./cu.m. of CO,absorbed.

It will finally be observed that the vapor extracted in the expansioncolumn C contains only a fraction of the CO absorbed. In some cases,therefore, when it is not necessary to recover all the'CO,, the vaporextracted from the expansion column may be passed directly to theatmosphere with a resultant saving on the size of the CO cooler.

The advantages demonstrated by the present example reside basically inthe fact that a) the purification of the gas takes place in a singlestage and a degree of purity is achieved which, by the hitherto knowntechniques, would have required a two stage cycle; b) the supply of heatand consequently the dimensions of the reboiler are approximately closeto half; also the size of the regenerator is consequently reduced; c) asstated above, the CO, cooler may also be made smaller if total recoveryof the CO, absorbed is not required.

EXAMPLES 2 AND 3 Here are given two parallel examples of practicalapplication, along the lines set forth in section 2.

The two examples are shown in FIGS. 17 and 18 respectively. Both relateto the decarbonatation of a gaseous mixture containing 18 percent CO,and at a pressure of 29 atm. by a potassium arsenite solution containing200 g/l K 0 and 140 g/l AS503. In both cases, the solution isregenerated in the regenerator R by the supply of 26,400 kg.cal./cu.m.of solution which corresponds to having a regenerated solution with adegree of 10 percent carbonatation. In both cases, the regeneratedsolution, with an initial temperature of l 10C, is treated in thevaporization chamber C so as to extract from it a current of vaporcorresponding to cooling of the solution to approx. 85C, so obtaining animprovement in the degree of regeneration of the solution to 2 percent(see FIG. 13). It is however noted that in practice, substantiallybetter figures were often obtained.

In the cycle referred to in FIG. 17, the stream of vapor thus extractedis discharged to outside without being further used, while the solutionemerging from the vaporization zone or chamber C is passed without beingfurther cooled (being already cooled to 85C) to the top of the absorberA where it purifies the gaseous mixture down to 0.1% C0,. The solution,descending through the absorber, becomes heated by the heat of reactionand by the heat content of the gas (supplied at 120C, which is thetemperature at which it leaves the I reboiler) up to 98C, reaching adegree of carbonatation of 64 percent and being passed directly to theregenerator. In keeping with the variation in the degree ofcarbonatation, 64% 2%, the charge containing solution is 29.5 parts CO,per part of solution and the consumption of heat is 895 kg.cal./nominalcu.m. CO

In the cycle referred to in FIG. 18, on the other hand, the current ofvapor extracted from the chamber C is passed to the chamber-C where itis used for heating the exhausted solution originating from the bottomof the absorber A. Consequently, it has been possible to diminish theabsorption temperature and in fact the regenerated solution is cooleddown to 58C in the cooler F and passed to the top of the absorber A,where it purifies the gaseous mixture down to 0.05 percent CO as itdescends through the absorber, it becomes heated up to C by the heat'ofreaction and by the heat in the gaseous mixture whichis supplied at C,and reaches a degree of carbonatation of 73.5 percent; it is finallypassed into a chamber C where it is heated by the stream of vaporemerging from the chamber C; it is subsequently passed into theregenerator. In keeping with the variation in the degree ofcarbonatation from 73.5 percent to 2 percent, the charge in the solutionis 34 parts CO, per part of solution and the consumption of heat is 770kg.cal./nom.cu.m. of C0,.

In order to extract the current of vapor from the vaporization chambers,vacuum pumps were used, denoted by reference letters M1, M2, the saidpumps being applied on the streams of vapor emerging from thevaporization chambers.

The advantages of the present invention, clearly disclosed by the twoforegoing examples, can be summarized as follows:

a. Reduction in the regeneration heat; The heat required to regenerate Icum. of solution to a degree of carbonatationof percent is 26,400kg.cal., whereas the heat required to regenerate it down to 2 percentcarbonatation is 40,500 kg.cal. The invention allows the solution to beregenerated down to 2 percent carbonatation by the amount of heatnormally required to achieve 10 percent carbonation. This represents asaving of 14,100 kg.cal./cu.m. of solution, in other words approx. 35percent.

. The single stage cycle is sufficient to achieve purification to 0.05to 0.1 percent C0,, with a consumption of heat substantially below 1,000kg.cal./nom.cu.m. C0,; in the known techniques, this necessitated atwo-stage cycle. This advantage is obviously of fundamental importance.

. It will be observed that in example 3 which employs a conventionalcycle in which the absorption temperature is substantially less than theregeneration temperature, the heat exchanger between the regeneratedsolution and theexhausted solution is eliminated.

Example 2 on the other hand uses the optimum cycle as stated atthebeginning of the present description.

EXAMPLE 4 Example 4 relates to a practical embodiment in which theejector is used.

This exemplary embodiment is entirely similar to example 3 referred tohereinabove. with reference to FIG. 16, the ejector Ireplaces the vacuumpump M1 and the mixing chamber C in FIG. 4. In it, as will be readilyunderstood by a man skilled in the art, the exhausted solutionoriginating from the absorber, traverses the ejector I in which itcreates a negative pressure which is exerted on the vaporization chamberC from which it extracts a stream of vapor which becomes blended in theejector itself and in the subsequent chamber so as to heat the solutionbefore this latter is introduced into the regenerating column.

The remaining'details concerning operation of the plant are similar tothose set forth in example 3.

EXAMPLES 5 AND 6 to having a solution regenerated to percent C( content.

The solution extracted from the bottom of the regenerator is treated bya current of inert gases with which it is brought into intimate anddirect contact in the vaporization chamber C in which the solution iscooled down to 85C and is regenerated to a 4% CO, content. During thistreatment, it has been established that it is necessary to use 4 cu.m.of inert gas per cu.m. of solution and it is observed that this quantityof inert gas is readily available in the waste from ammonia synthesis(in other words waste which is used to avoid the accumulation of methaneor other inert gases in the gases circulating in the synthesizingplant).

According to the cycle illustrated in FIG. 20, the solution which, aftertreatment with the inert gases, is regenerated to a degree ofcarbonatation of 4 percent and is cooled down to 85C, is passed directlyand without further cooling to the absorption column A where a degree ofpurification to 0.10% CO, is attained. Subsequently, the solutiondescends through the absorber, reaching at the bottom a temperature of98C due .to the heat of reaction and the heat contained in the gas to bepurified, which is fed in at a temperature of 120C as it emerges fromthe reboiler. The solution at this temperature is finally passeddirectly into the regenerating column, completing the cycle. The inertgases on the other hand, after being treated in intimate and directcontact with the exhausted solution in the chamber C, are discharged tothe outside.

The solution which, at the bottom of the absorber,

attains a degree of carbonatation of 71 percent, has a charge of 32parts CO, per part of solution; the heat consumption is 675kg.cal./cu.m. C0,.

According to the cycle illustrated in FIG. 19, on the other hand, theinert gases, after having been brought into intimate and direct contactwith the solution regenerated in zone C, from which they emerge heatedand humidified, are passed into the zone C where they are used to heatthe exhausted solution emerging at the bottom of the absorber. This hasmade it possible advantageously to reduce the absorption temperature.Consequently, the regenerated solution is subsequently cooled from 85Cto approx. 60C and passed to the top'of the absorber A where it purifiesthe gaseous mixture down to 0.05 percent C0,; subsequently, descendingthrough the absorption column A, it becomes heated to C due to the heatof reaction and the heat in the gaseous mixture. It is subsequentlypassed into the zone C' where the current of inert gases originatingfrom C heats it to a temperature of approx. 94C and eliminates aquantity of C0,, regenerating the solution down to a carbonatation levelof 35 percent. Finally, it passes to the regenerating column.

In this example, the charge in the solution is 37 parts CO, per part ofsolution and the consumption of heat is 585 kg.cal.lcu.m.'CO,.

It should be noted that the current of inert gases which have eliminatedthe CO, both from the regenerated solution and possibly also from theexhausted solution is discharged into the atmosphere. This constitutes areduction in the quantity of CO, emerging from the regenerator andavailable for other purposes. In the first case, FIG. 20, the CO, lostis a substantial fraction of the total while in the second case, FIG.19, it is only 16.5 percent.

As will be known to a man skilled in the art, the first case representsthe application of a conventional cycle in which, in addition toimproving the regenerative effect obtained by the treatment with inertgases in the regenerated solution, it is also possible to dispense withthe heat exchanger between the regenerated solution and the exhaustedsolution; in the second case, on the other hand, the optimum cycle isapplied in which, in addition to improving the regenerative effect ofthe regenerated solutions, there is the advantage that the absorptiontemperatures vary within 85 and 100 approx., becoming advantageouslyclose to the optimum absorption temperatures.

EXAMPLE 7 This example relates to the case where a monoethanol aminesolution is used. In a conventional CO purification plant employing theconventional cycle and using monoethanol amine solution in aconcentration of 2.5 mols/liter, it should be noted that the solution ispassed to the head of the stripper at a temperature of 96C. approx.(205F) and emerges at the bottom of the regenerator with a CO, contentof 0.14 mols CO per mol MBA and at temperature of 120C (248F).Subsequently, the regenerated solution, passing in counter currentthrough a heat exchanger, heats the exhausted solution emerging from theab sorbet to a temperature of 96C, as stated above.

The above-mentioned plant is modified and improved as follows:

a. The solution is regenerated in the regenerating column to a C contentof 0.1 8 mols CO, per mol MBA with a corresponding saving on the supplyof heat to the reboiler. Subsequently, the solution is treated in anexpansion chamber using negative pressure generated by a vacuum pump andis cooled to approx. 100C (212F), eliminating C0 and attains a C0content of 0.14 mols per mol MEA, which was the level attained in theplant operating by the conventional system.

The vapor extracted by the vacuum pump is brought into intimate anddirect contact with the exhausted solution emerging from the absorber,heating it to approx. 96C. In the event of the solution originating fromthe absorber at a temperature of approx. 85C (185F), a single heatingand mixing stage is adequate between the extracted vapor and theexhausted solution and this is sufficient for the heat exchanger to becompletely eliminated. On the other hand, if the exhausted solutionemerges from the absorber at a lower temperature, it is still possiblepartially to use the exchanger or an apparatus may be used for heatingand mixing the vapor and solution in multiple stages, as indicated inFIG. 21.

The scheme can be particularly simplified by using the ejector in whichuse is made of the energy contained in the exhausted solution. Thismakes it possible to dispense with the vacuum pump while the ejectoritself can operate as a heating and mixing chamber.

EXAMPLE 8 This example concerns the elimination of hydrogen sulphide bymeans of solutions of diethanolamine in a concentration of 2 N/liter.

The installation employing the conventional layout provides for thetemperature at the top of the regenerating column to be about 98C.(208F.) and for the temperature at its base to be about l24C. (256F.).The solution is withdrawn from the base of the column at the saidtemperature and has a content of approx. 0.12 mol. of hydrogen sulphideper mol. of amine. With reference to FIG. 18, the solution is fed intothe expansion chamber C, where it is subjected to a pressure dropcreated by suitable mechanical means M2 and cooled to a temperature ofabout C. (212F.). in these conditions, the steam extracted from thesolution is practically free from acid gases and hence is utilized inthe heating chamber C in the best of conditions for there heating theexhausted solution taken from the absorption column.

The exhausted solution reaches the heating chamber C at a temperature of74C. (l65.2F.) and is heated to a temperature of 96C. (204.8F.) and thenpassed to the top of the regenerator column. The heating of theexhausted solution from the temperature of about 40C. (104F.), as itarrives from the absorption column, to the temperature of 74C. iseffected by means of a partial heat exchanger, in which it is broughtinto contact with the regenerated solution leaving the expansion chamberC. In this way, the exchanger in the conventional cycle is partlyeliminated. If desired, the exchanger can be eliminated altogether byadopting the arrangement shown in FIG. 21.

The above example is parii'ciflarifmairtagous using the ejectorfollowing the heating chamber C, in which the heating of the solutionproduces only slight evolution of acid vapor, which have no undue effecton the performance of the ejector.

We claim:

il In a process of eliminating acid gases selected from the groupconsisting of C0 H 8 and mixtures thereof from gaseous mixturescontaining them, using a regenerable absorbent solution which iscirculated between an absorption zone in which the solution is broughtinto intimate and direct contact with the gaseous mixture in order topurify it and to eliminate said acid gases from it and a regeneratingzone in which the solution is brought to the boil by externally suppliedheat, with the expulsion of said acid gases previously absorbed, theimprovement which comprises:

passing the hot and boiling solution extracted from the regeneratingzone and containing rc sidual abar sadism gases to an expansion zonemaintained at a pressure substantially lower than the pressure existingin the regenerating zone; generating from the solution undergoingexpansion a stream of vapor; eliminating with the said stream of vaporpart of said acid gases still contained in the solution itself and inthus cooling the solution; restoring the thus cooled solution which hasa lesser content of said acid gases to the absorption zone; passing -thestream of vapor together with said acid gases extracted from thesolution to a heating zone;

passing to the said heating zone the exhausted solution originating fromthe absorber and bringing it into intimate and direct-contact with thevapor, with resultant heating of the solution and condensation of thevapor;

extracting the solution from the heating zone and v passing it into theregenerating zone; and discharging the said acid gases from the system.

2. In a process of eliminating acid gases selected r l9 regenerableabsorbent solution which is circulated between an absorption zone inwhich the solution is brought into intimate and direct contact with thegaseous mixture in order to purify it and eliminate said acid gases fromit and a regenerating zone in which the solution is brought to the boilby externally supplied heat with the expulsion of said acid gasespreviously absorbed, the improvement which comprises:

passing the hot and boiling solution extracted from the regeneratingzone and containing residual absorbed acid gases to a vaporization zone;passing a current of inert gases into the saidvaporization zone;bringing the said current of inert gases into intimate and directcontact with the solution; extracting therefrom a stream of vapor andeliminating part of said acid gases still contained in the solutiontogether with the said stream of vapor and inert gases whereby thesolution is cooled; restoring the-thus cooled solution which has alesser content of said acid gases to the absorption zone; extractingfrom the vaporization zone the stream of vapor and inert gases togetherwith said acid gases eliminated from the solution;

passing the said stream of vapor and inert gases together with said acidgases to a heating zone;

passing the exhausted solution emerging from the absorber into the saidheating zone and bringing into intimate and direct contact with thevapor, with resultant heating of the solution and condensation of thevapor;

extracting the solution from the heating zone and passing it to theregenerating zone; and

dischargifiisaid acid gases from the system.

3. In a process as claimed in claim 1, the further improvement whichcomprises using an expansion zone from which the stream of vapor andsaid acid gases are extracted composed of successive stages whereby thevapor and said acid gases extracted from each individual stage of thesaid zone is passed to successive and corresponding stages in theheating zone in contact with the exhausted solution.

a a x. a

UNnEn STATES PATENT OFFICE I CERTEFKCATE @i (IQRFRECTIQN Patent No. 3,714, 327 Dated January 30, 1973 Inv n 0 Giuseppe Giarmnarco It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In The Heading:

The Assign'ee's name was omitted. Should read:

--Assignee: Vetrocoke Cokapuania S. p. A. Venez ia Porto Marghera, Italy(one half)-- The Priority Date was omitted. Should read:

--Italy October 15, 1968........ 53496 A/68 Italy April 19, l969...-...5 A/69 w Signed and sealed this 3rd day of July 1973.

(SEAL) Attest 2 EDWARD M.FLETCHER,JR. Rene Tegtmeyer Attesting OfficerActing Commissioner of Patents USCOMM 'DC 6O376-P69 U.S. GOVERNMENTPRINTING OFFICE I955 O366-334,

1. In a process of eliminating acid gases selected from the groupconsisting of CO2, H2S and mixtures thereof from gaseous mixturescontaining them, using a regenerable absorbent solution which iscirculated between an absorption zone in which the solution is broughtinto intimate and direct contact with the gaseous mixture in order topurify it and to eliminate said acid gases from it and a regeneratingzone in which the solution is brought to the boil by externally suppliedheat, with the expulsion of said acid gases previously absorbed, theimprovement which comprises: passing the hot and boiling solutionextracted from the regenerating zone and containing residual absorbedacid gases to an expansion zone in which mechanical means are used toapply negative pressure; generating from the solution undergoingexpansion a stream of vapor; eliminating with the said stream of vaporpart of said acid gases still contained in the solution itself and inthus cooling the solution; restoring the thus cooled solution which hasa lesser content of said acid gases to the absorption zone; passing thestream of vapor together with said acid gases extracted by mechanicalmeans from the solution to a heating zone; passing to the said heatingzone the exhausted solution originating from the absorber and bringingit into intimate and direct contact with the vapor, with resultantheating of the solution and condensation of the vapor; extracting thesolution from the heating zone and passing it into the regeneratingzone; and discharging the said acid gases into the outside ambient. 2.In a process of eliminating acid gases selected from the groupconsisting of CO2, H2S and mixtures thereof from gaseous mixturescontaining them, using a regenerable absorbent solution which iscirculated between an absorption zone in which the solution is broughtinto intimate and direct contact with the gaseous mixture in order topurify it and eliminate said acid gases from it and a regenerating zonein which the solution is brought to the boil by externally supplied heatwith the expulsion of said acid gases previously absorbed, theimprovement which comprises: passing the hot and boiling solutionextracted from the regenerating zone and containing residual absorbedacid gases to a vaporization zone; passing a current of inert gases intothe said vaporization zone; bringing the said current of inert gasesinto intimate and direct contact with the solution; extracting therefroma stream of vapor and eliminating part of said acid gases stillcontained in the solution together with the said stream of vapor andinert gases whereby the solution is cooled; restoring the thus cooledsolution which has a lesser content of said acid gases to the absorptionzone; extracting from the vaporizatioN zone the stream of vapor andinert gases together with said acid gases eliminated from the solution;passing the said stream of vapor and inert gases together with said acidgases to a heating zone; passing the exhausted solution emerging fromthe absorber into the said heating zone and bringing into intimate anddirect contact with the vapor, with resultant heating of the solutionand condensation of the vapor; extracting the solution from the heatingzone and passing it to the regenerating zone; and discharging said acidgases into the outside ambient.